The chemical nature of the labile selenium moiety in erythrocyte glutathione peroxidase, a selenoprotein, will be studied by purification of low molecular weight fragments from the degraded protein. Additional studies on forms of selenium in brain and their interactions with methylmercury, a CNS poison, will be performed to see if selenoproteins having important functions can be identified that may be targets of methylmercury. The purification and characterization of a 30,000 MW testicular Cd-binding protein will also be undertaken in order to better understand the mechanism of Cd-induced testicular necrosis. Bibliographic references: Hsieh, H. Steve, and Ganther, H.E. "Acid- volatile Selenium Formation Catalyzed by Glutathione-Reductase" Biochemistry 14:1632-1636 (1975). Wagner, P.A., Hoekstra, W.G., and Ganther, H.E. "Alleviation of Silver Toxicity by Selenite in the Rat in Relation to Tissue Glutathione Peroxidase." Proc. Soc. Exp. Biol. Med. 14:1106-1110 (1975).